1. Field of the Invention
The present invention relates to a control system of an industrial truck and a controlling method of the same. More particularly, the present invention relates to a control system of the industrial truck and the controlling method of the same for an industrial truck such as a fork-lift truck.
2. Description of the Related Art
It is known that industrial trucks (vehicles), such as a fork-lift and a truck crane, work to lift and move loads by applying force as external forces directly to the loads. When these industrial trucks are operated, an operating condition for their machine elements is required to be more strict than for automobiles, such as a passenger motor car. Automobiles transport persons and luggage, but they do not apply their force directly to persons and luggage. One of the required operating conditions is a safety condition regarding safe operation. In the passenger motor car, wheel stoppage is the important safety condition. In addition, the relation between a wheel rotation state and a machine operation state is also an important safety condition in an industrial truck.
In conjunction with the above description, Japanese Laid Open Patent Application (JP-A-Heisei 07-76498) discloses the following industrial truck. In this industrial truck, safety is secured by considering a positioning relation between the industrial truck body and its operator (driver). The industrial truck includes a seat switch that outputs a seating signal corresponding to the seating of the operator on the seat of the body. The existence of the seating signal outputted by the seat switch is one element of a machine operation enabling condition. The non-existence of the seating signal (including the non-existence of the delayed seating signal) is one element of a machine operation disabling condition. This industrial truck achieves both high safety and operability.
The non-seating signal, which is outputted when the operator does not sit on a seat, can be effectively utilized. It is effective to prepare a control valve for controlling a hydraulic pressure distribution of the work machine in order to prohibit or limit the machine operation corresponding to the non-seating signal. An industrial truck with such a control valve is disclosed in Japanese Laid Open Patent Applications S64-60598, S64-60599 and U.S. Pat. No. 5,577,876.
When outputting the non-seating signal, preventing hydraulic oil in the hydraulic pressure cylinder from returning by mechanical control of the control valve should be important to secure desired safety. It is desired for simplifying a hydraulic circuit to take advantage of the conventional mechanical controlling function of the control valve.
The following are discussions of the Japanese Laid Open Patent Applications and the U.S. Patent described above.
A control method of a control valve for landing and loading for a vehicle is disclosed in the Japanese Laid Open Patent Application S64-60598. In this control method, the vehicle is controlled by preparing a switch valve in either of a pilot hydraulic oil pipe route and two pilot drainpipe routes, or in both. The control valve for landing and loading in the vehicle is controlled at the hydraulic pressure control circuit. Here, the pilot hydraulic oil pipe route provides pilot hydraulic oil to the spool of the control valve, which controls a decompression actuator. The pilot drain pipe route is prepared in response to the pilot hydraulic oil pipe route and is used for providing the pilot hydraulic oil. The switch valve is opened and closed by an electric signal which is outputted from the control apparatus on the basis of an operation signal, a seating signal and an auxiliary operation signal. The operation signal corresponds to the operation of means for landing and loading operation. The seating signal, in response to detecting that the operator sits on the seat, is outputted from the seat switch. The auxiliary operation signal is outputted from an auxiliary switch which the operator can use arbitrarily when he does not sit. The control valve for landing and loading in the vehicle is controlled by this control method as follow. When the seating signal or the auxiliary operation signal are inputted to the control apparatus continuously for a predetermined time, a control signal which corresponds to the operation of the means for carrying out the landing and loading operation is outputted to the switch valve. When the means of landing and loading operation is operated before the seating signal, or the auxiliary operation signal is inputted to the control apparatus, or when the seating signal or the auxiliary operation signal is inputted to the control apparatus during the operation and the input continues for a predetermined time, the control signal, in low level, is outputted to the switch valve at first, and the level of the control signal is gradually raised in accordance with the present amount of operation of the means of landing and loading.
Further, a control method of a control valve for landing and loading for vehicle is also disclosed in Japanese Laid Open Patent Application S64-60599 as a related technique. In this control method, the vehicle is controlled by preparing a switch valve in either of a pilot hydraulic oil pipe route and two pilot drain pipe routes, or in both. The control valve for landing and loading in the vehicle is controlled at the hydraulic pressure control circuit. Here, the pilot hydraulic oil pipe route provides pilot hydraulic oil to the spool of the control valve, which controls a decompression actuator. The pilot drain pipe route is prepared in response to the pilot hydraulic oil pipe route and is used for providing the pilot hydraulic oil. The switch valve is opened and closed by an electric signal which is outputted from the control apparatus on the basis of an operation signal, a seating signal and an auxiliary operation signal. The operation signal corresponds to the operation of means of landing and loading operation. The seating signal, in response to detecting that the operator sits on the seat, is outputted from the seat switch. The auxiliary operation signal is outputted from an auxiliary switch which the operator can use arbitrarily when he does not sit. The control valve for landing and loading in the vehicle is controlled by this control method as follows. When the seating signal from the seat switch or the auxiliary operation signal from the auxiliary switch are inputted to the control apparatus, a control signal which corresponds to the operation of the means of landing and loading operation is outputted to the switch valve. When the means of landing and loading operation is operated before the seating signal from the seating switch or the auxiliary operation signal from the auxiliary switch is inputted to the control apparatus, or when the seating signal or the auxiliary operation signal is inputted to the control apparatus during operation, the control signal, at low level, is outputted to the switch valve at first, and the level of the control signal is gradually raised in accordance with a present amount of operation of the means of landing and loading.
Further, a control apparatus of a fork-lift is disclosed in Japanese Laid Open Patent Application H7-76498 as a related technique. The fork-lift includes a seating switch which is switched ON and OFF according to the seating or non-seating of the operator. The control apparatus determines permission or prohibition of the operation of the machine for loading and landing work on the basis of the ON/OFF state of this seating switch. The operation is possible to be permitted immediately when the seat switch switches to either state of ON and OFF by the operator's seating. On the other hand, being switched to the other by an operator's standing, and continuing in this state for a predetermined time, results in the operation being prohibited.
Furthermore, in conjunction with the above description, U.S. Pat. No. 5,577,876 discloses the following technique. In a skid steer loader of the type having a control apparatus for controlling movement of a lift arm on the skid steer loader, an improvement includes a power actuator means, a hydraulic power circuit, a sensor, a power interruption means and manually operable bypass means. The power actuator means is coupled to the lift arm for moving the lift arm along a path. The hydraulic power circuit is coupled to the power actuator means, providing hydraulic power to the power actuator means, along a first power path, to move the lift arm in a first direction. The sensor is coupled to the skid steer loader for sensing a desired parameter and providing a sensor signal indicative of the desired parameter. The power interruption means includes a first hydraulic valve coupled in the first power path to the power actuator means and the sensor for interrupting power to the power actuator means based on the sensor signal. The manually operable bypass means includes a second hydraulic valve coupled to the hydraulic power circuit and the power actuator means for providing a second power path between the hydraulic power circuit and the power actuator means, bypassing the power interruption means to allow movement of the lift arm.